awk Simple Application explanation

Gawk:pattern scanning and processing language

Syntax: gawk [options] ' program ' FILE ...

Program:pattren{action statements}

Options:

-F: Indicates the field delimiter when entering data

-V var=value: Custom variable

1. Print

Print item1,item2, ...

Key points: (1) Comma delimiter

(2) Each item of the output can be a string, a value, a field (using & Reference), a variable (directly input a variable), or an awk expression

(3) If item is omitted, it is equivalent to print $

2. Variables

built-in variables

fs:input field seperator input delimiter: default to white space character

Ofs:onput field seperator output delimiter: Default to white space character

Rs:input record seperator: line break at input

Ors:output record seperator: line break at output

Nf:number of field: Number of fields per row

Nr:number of Recor: Rows

FNR: Each file counts: number of rows

FileName: Current file name

ARGC: Number of command-line arguments (use begin to show only once before the command)

ARGV: Array argv[#]: Saves the parameters given in the command line

Custom variables

(1)-V var=value case-sensitive

(2) directly defined in program

awk ' {test= ' 1 ";p rint test} ' filename

If the file is not processed: awk ' begin{test= ' 1 ";p rint test} '

3. printf command

Formatted output: printf format (format character), ITEM1,ITEM2, ...

(1) FORMAT must give the

(2) does not wrap automatically, need to display the line feed control \ n

(3) format needs to specify a formatting symbol for each subsequent item, respectively

Format characters:

%c: ASCII code for displaying characters

%d,%i: Displaying decimal integers

%e,%e: Numerical display of scientific counting method

%f: Floating point

%g,%g: Scientific counting method or floating point number

%s: string

%u: unsigned integer

Percent: show% itself

Modifier:

#[.#]: The width of the first digital control display, the second shows the precision after the decimal point (%3.1f)

-: Left-justified, default right-justified

+: Displays the value of the symbol (plus or minus)

4. Operator

arithmetic operators

Binocular: +-*/^%

Monocular:-X +x

String operator: unsigned operator, string connection

Assignment operator: = + = = *= ...

Comparison operators: > >= < <= = = =

Pattern match: ~ match

！ ~ No match

Logical operator:&& | | !

Function call: function_name (ARGU1,ARGU2,...)

Conditional expression: select?if-true-expression:if-false-expression

5. Pattern

(1) Empty: null mode, matching each row

(2)/regular expression/: Regular expression, processing only matching rows

(3) conditional expression/relationship expression: The result is "true" "false" and the row with the result is "true"

True: The result is a non-0 value, non-empty string

(4) line ranges: Range

STARTLINE,ENDLINE:/PAT1/,/PAT2/indicates a range by pattern matching

Formats that give numbers directly are not supported

Awk-f: ' (nr>=2&&nr<=10) {print '} '/etc/passwd

(5) Begin/end mode

begin{}: A program that executes only once before beginning the processing of text in a file

end{}: Only once after text processing is complete

6. Common action

(1) expressions

(2) control statements:if,while, etc.

(3) Compound statements: Combined statement:

(4) Input statements

(5) Output statements

7. Control statements

if (condition) {statements} else {statements}

while (conditon) {statements}

do {statements} while (Conditon)

for (expr1;2;3) {statements}

Break

Continue

Delete Array[index]

Delete Array

exit

{Statements}

Example:

1,-F: Indicates the field delimiter when entering data, and defaults to white space characters. The example uses ":" as a delimiter and outputs the first set of elements:

[Email protected] ~]# Tail-n 5/etc/passwd | Gawk ' {print $} ' Pulse:x:497:496:pulseaudiosshd:x:74:74:privilege-separatedtcpdump:x:72:72::/:/sbin/nologinarmo: X:500:500:centosnamed:x:25:25:named:/var/named:/sbin/nologin[[email protected] ~]# tail-n 5/etc/passwd | Gawk-f: ' {print '} ' pulsesshdtcpdumparmonamed

2,-v Var=value and begin use: Separate begin does not process text, only output actions, combined with the use of custom variables: (You can use the option definition, but also directly in the program defined variables)

[[email protected] ~]# awk-v Test=armo ' begin{print test} ' armo[[email protected] ~]# awk ' begin{test= ' Armo ';p rint test} ' Armo

3, the use of built-in variables: NR: Display line number

[Email protected] ~]# Tail-n 5/etc/passwd | Awk-f: ' {print nr,$1,$2} ' 1 pulse x2 sshd x3 tcpdump x4 Armo x5 named X[[email protected] ~]#

4. Formatted output of printf

[[email protected] ~]# awk -f:  ' {printf  ("%s,%s\n", $1,$2)} '  /etc/passwdroot , xbin,xdaemon,xadm,xlp,x ... [[email protected] ~]# awk -f:  ' {printf  ("%15s    --%5s\n", $ 1,$2)} '  /etc/passwd           root     --    x             bin    --    x          daemon    --    x             adm    --    x              lp    --    x            sync    --     x       shutdown    --    x            halt    --     x           mail    --     x First domain character width 15, second field character Wideband 5[[email protected] ~]# awk -f:  ' {printf   ("%-15s%+5.3f\n", $1,$3)} '  /etc/passwdroot            +0.000bin            +1.000daemon          +2.000adm             +3.000lp              +4.000sync           +5.000shutdown        +6.000 first field left-aligned width 15 output, third field displays numeric positive and negative, width 5, decimal point accurate to three-bit output 

4. Examples of operator usage instructions

[[email protected] ~]# awk-v a=2-v b=1 ' Begin{print "sum=" a+b} ' sum=3[[email protected] ~]# awk-f:-v a=2-v b=1 ' {$3&G T;=5? Sum=a+b:sum=a+a;print $1,sum} '/etc/passwdroot 4bin 4daemon 4adm 4lp 4sync 3shutdown 3halt 3mail 3UUCP 3

5. Pattern Example

[Email protected] ~]# awk-f: ' (nr>=2&&nr<=10) {print nr,$1} '/etc/passwd2 bin3 daemon4 adm5 lp6 sync7 Shutd OWN8 halt9 mail10 uucp[[email protected] ~]#

awk Simple Application explanation